Production of iron having valuable magnetic properties



Patented Apr. 20, 1932 ENHTEE. STATES lessee rarest crates FRANZ DUFTSCHMID, OF HEIDELBERG, AND LEO SCHLECHT, OF LUDWIGSHAFEN-ON- THE-RHINE, GERMANY, ASSIGNORS TO I. G. FARBENINDUSTRIE AKTIENGESELL- SCHAIET, OF FRANKFORT-ON-THE-MAIN, GERMANY PRODUCTION OF IRON HAVING VALUABLE MAGNETIC PROPERTIES No Drawing. Application filed August 9, 1930, Serial No. 474,307, and in Germany August 28, 1929.

The present invention" relates to the pr0- duction of iron having valuable magnetic properties.

In the production of iron having valuable 5 magnetic properties it has hitherto only been possible to obtain initial permeabilities of 500 and more by fusing purestelectrolytic iron in vacuo. In this way it is possible to obtain initial permeabilities amounting to 1000, but only while maintaining such great precautions that an industrial production is pre cluded.

We have now found that iron having excellent magnetic properties is obtained by subjecting iron in lump form which has been obtained from finely divided iron by a sintering treatment by the application of mechanical pressure and/or heat, preferably in an treatment by heat in vacuo below its melting point at temperatures of at least 400 C., preferably between 600 and 900 C., and most suitably attemperatures only slightly below 900 C. For the production of such very valuable magnetic iron, iron powder which has been obtained from iron carbonyl and which preferably contains carbon, or finely divided iron which has been obtained from iron chloride by reduction with hydrogen is especially suitable.

In order to produce iron having particularly good magnetic properties it is advantageous to subject the pieces of consolidated iron powder to one or more preliminary treatments by heat under atmospheric or elevated pressure and at temperatures between 400 C. andthe melting point of the iron, preferably in a hydrogen-atmosphere, prior to the treatment by heat in vacuo. The heat treatment in vacuo is advantageously carried out at temperatures below the Ac point, i. e. below 900 C. Prior to the treatment by heat in vacuo or prior to the saidpreliminary heat treatment, the pieces of irbn are preferably worked in the cold to such an extent that the formation of large and uniform crystals is eflected by the subsequent heat treatment or treatments, any of which likewise is preferably carried out at temperatures below, but preferably only slightly below 900 C.

atmosphere of hydrogen, without fusion, to a' The working in the cold may be effected by rolling or stretching. The attainable size of grain depends not only on the purity of the material and on the manner of carrying out the subsequent treatment by heat but in particular also on the degree of deformation in the cold, It is referable to maintain a degree of deformation of between 2 and 30 per cent, whereby under the same conditions for the subsequent treatment by heat iron crystals are obtained which are the greater, the smaller the degree of deformation. It has been found that the magneticproperties of the iron, especially its initial permeability, depend on the size of the grains in that the magnetic properties are the better, the larger the grains. 7 If the material is several times worked in the cold, it is the last deformation in the cold that influences the size of the grains and thus is decisive as to the magnetic properties of the material.

The iron obtained according to the present invention is characterized in particular by high initial permeability, high maximum permeability, small coercive force and small hysteresis loss. For example sheets may easily be prepared which have an initial permeability of between 1000 and 2500 and a coerciv'e force below 0.15 gauss. The advantages of the invention will be obvious from the fact that it is possible when working according to the process described to produce unalloyed iron in pieces having an initial permeability higher than 2500 and having a coercive force of 0.10 gauss. According to the methods hitherto known it is only possible to prepare a material having an initial permeability of not more than 1150 from electrolytic iron. This material may be employed with advantage for the construction of electrical apparatus in which the said magnetic properties are especially desirable, as for example transformers, measuring instruments and the like.

The following examples will further illustrate the nature of this invention, but the invention is not restricted thereto.

Example 1 Ironpowder produced by decomposition of iron carbonyl having a content of 1.2 per cent of carbon and 1.2 per cent of oxygen but which is free fromother impurities is simultaneously sintered, decarbonized and reduced 5 by heatin to a temperature of 650 C. in a current 0 hydrogen. The sintered material is then further heated to 1100 C. in an atmosphere of hydrogen and with this initial temperature it is then rolled into sheets one millimeter in thickness. The sheets which have been rolled while hot are glowed in a current of hydrogen, rolled out while cold each to a thickness of 0.5 millimeter and then glowed at 850 C. for 24 hours in vacuo. Sheets which have been obtained and treated in the manner described have the following magnetic constants: initial permeability=1000, maximum permeability=14500, coercive force 0.19 gauss, remanence 5200- Example 2 Iron powder obtained by thermal decomposition of iron carbonyl, containing 1.2 per cent of carbon and 1.2 per cent of oxygen is sintered, decarbonized and reduced by heating it in a current of hydrogen at 650 C.

The sintered material is heated at 1200 C. in a hydrogen atmosphere and worked up at the said temperature by rolling in the air to sheets of 1 millimeter thickness.

After a heat treatment of the sheets thus obtained in a current of' hydrogen at 800 C.

the thickness of the sheets is further reduced to 0.5 millimeter by cold rolling. These sheets are then heated at 850 C. fore hours I in a current of hydrogen and then rolled, while cold, to sheets of a thickness of 0.48, 0.45 and 0.40 millimeter respectively, the sheets being then again heated at 850 C. for 12 hours in vacuo. The crystals of the sheets thus produced have an average diameter of 8, 3 and 1.5 millimeters respectively and the initial permeability of the iron thus obtained is 2500, 1800 and 1450 respectively, the maxi mum permeability being 19000, 15200 and 13900 respectively.

What we'claim is 1. A process for the production of iron having valuable magnetic properties which comprises subjecting iron in lump form which has been obtained from finely divided iron by a ing valuable magnetic properties which comprises sub ect ng iron in lump form preparedfrom iron powder which has been obtained from iron carbonyl by a sintering treatment without fusion, to deformation in the cold, then to a treatment by heat in a hydrogen atmosphere under at least atmospheric pressure and then to a treatment by heat in vacuo below 900 C.

6. A process for the production of iron having valuable magnetic properties which comprises subjecting iron in lump form prepared from iron powder which has been obtained from ironcarbonyl and which contains carbon, by a sintering treatment without fusion, to deformation in the cold, then to a treatment by heat in a hydrogen atmosphere under at least atmospheric pressure and then to a treatment by heat in vacuo below 900 C.

7. As a new article of manufacture, unalloyed iron in lump form which has an initial permeability substantially exceeding 1150.

8. As a new article of manufacture, unalloyed iron in lump form which has an initial permeability of at least 1450.

. In testimony whereof we have hereunto set our hands.

FRANZ DUFTSCHMID. LEO SCHLECHT.

sintering treatment without fusion, to a treatment by heat in vacuo.

2. A process for the production of iron hav- 7 56 ing valuable magnetic properties which comprises subjecting iron' in lump form which has been obtained from finely divided iron I 

